CN102869959A - Ultrasonic flow meter - Google Patents

Abstract

The invention discloses an ultrasonic flowmeter, which includes a switching unit, which is used for switching the electrical transmission signal between a signal generator and at least two ultrasonic transducers, and for switching the electrical reception signal between the transducer and a receiver circuit , wherein the switching unit is coupled to the output terminal of the operational amplifier of the signal generator and the inverting input terminal of the operational amplifier of the receiver circuit. Furthermore, the invention discloses a method of characterizing an ultrasound transducer comprising the step of directly determining one or more quantities characterizing the transducer from one or more supply current signals of active elements of a signal generator. Furthermore, the present invention discloses a method for determining the time delay of ultrasonic signals in a flow path of an ultrasonic flowmeter, comprising the step of comparing physically transmitted, delayed and received signals with simulated non-delayed signals.

Description

Ultrasonic Flow Meter

technical field

The present invention relates to ultrasonic flow meters for measuring fluid flow, more particularly in the field of transit-time flow metering.

Background technique

In general, flow metering using the transit time method involves placing two ultrasonic transducers with a suitable mutual distance on the flow path where the fluid flow is measured. An ultrasonic signal (typically having a frequency of several megahertz and a duration of several microseconds) is transmitted from the first transducer to the second transducer through the fluid, and the first time of transmission is recorded. Next, a similar ultrasonic signal is transmitted through the fluid in the opposite direction, ie, from the second transducer to the first transducer, and the second transmission time is recorded. Knowing the physical distance between the two transducers, the difference between the two recorded transit times can be used to calculate the flow rate of the fluid flowing along the flow path. However, the calculated flow rate must be calibrated using a correction table that takes into account sound velocity and fluid viscosity. These properties are all temperature dependent and a correction table with temperature dependent correction values is sufficient when the fluid type is known.

One problem to face when working with this type of flow meter is that the transducer parameters not only change very easily between samples, but also over time and when the temperature changes. Such differences and variations alter the shape of the received signal, making it difficult to use this shape as a basis for calculating absolute transit times.

Ultrasonic flow metering has undergone tremendous evolution over the past 25 years, from a small number of laboratory instruments to very high volume production standard equipment. To the extent that the technical and commercial challenges have been overcome, the technology is now competitive with most other approaches, including mechanical meters, in many areas of flow metering. For example, high-precision flow meters that are now mass-produced are commonly used as water meters, calorimeters, gas meters, and other meters for billing purposes.

Some of the challenges that continue to have an impact are improving flow meters so that they are less sensitive to electrical and acoustic noise and still keep the meters stable and manufacturable without sacrificing cost and power consumption. Sensitivity to noise is reduced by increasing the signal-to-noise ratio, which is the most effective way to increase the signal.

Typical sources of acoustic noise in ultrasonic flow meters are edge and external vibrations in the flow current, both producing a fixed acoustic noise level independent of the ultrasonic waves generated by the meter itself. Susceptibility to acoustic noise can be reduced by increasing the acoustic signal generated by the transducer or changing the physical shape of the flow meter.

Electronic noise in ultrasonic flowmeters has many sources such as thermal noise, externally induced (via electromagnetic, electric or magnetic fields or through wires) voltages and currents, or internally induced (from other signals or clocks in the circuit) cross-coupling, Some of them are signal level dependent and some of them are independent of signal level. The most effective way to reduce susceptibility to electrical noise is by increasing the electrical signals involved, and by keeping the impedance of electrical nodes as low as possible, so that the effects of electrical noise sources are reduced.

Many different electronic circuits dealing with these subjects are known in the prior art, for example GB2017914 (Hemp), US 4,227,407 (Drost), DE 19613311 (Gaugler), US 6,829,948 (Nakabayashi), EP 0846936 (Tonnes) and EP 1438551 ( Jespersen), each has advantages and disadvantages.

The two last referenced documents (Tonnes and Jespersen) describe transducer coupling which has the advantage that the impedance seen by the transducer is the same in the transmission case as in the reception case. The discussion in these two patent documents explains that this feature is a prerequisite for the proven stability and manufacturability of the entire flow meter under real conditions, that is, without unrealistic concerns about matching between components in the meter requirements. The reason for this fact is that accurate impedance matching allows the flowmeter to fully exploit the law of reciprocity.

Although the correlation between reciprocal and stable flow metering has been known for many years, it is currently known that the correlation described in these patent documents is only sufficient to withstand the inherent tolerances of piezoelectric ultrasonic transducers to be able to produce A practical approach to stable flow meters.

The transducer coupling described in these two documents includes an impedance which has the function of converting the current signal received from the transducer into a measurable voltage signal. Unfortunately, as explained in further detail below, this impedance also limits the electrical signal that can be supplied to the transducer and, in order to generate the largest possible received voltage signal, limits the magnitude of the impedance to the ultrasonic transducer at In the range of 0.5 to 2 times the impedance at the frequency of interest.

Nakabayashi (US 6,829,948) has another approach where the generator and receiver are implemented by two different means, but in this configuration the received signal strength is sacrificed for stable results when changing the transducer parameters.

As described below, it is an object of the present invention to overcome the problems indicated above and to provide a stable, producible flow meter capable of transmitting a high acoustic signal.

Contents of the invention

The invention relates to a method for determining the absolute transit time of an ultrasonic signal in a flow path of an ultrasonic flowmeter comprising two ultrasonic transducers, said method comprising the following steps:

The supply current for the transducer is obtained by monitoring the current from one or more voltage supplies to the active components of the signal generator to drive the transducer during or after supplying the input signal to the signal generator Signal,

simulating a flowmeter response similar to the output signal from the receiver circuit of the flowmeter as an output signal if there is no time delay in the transmission of the ultrasonic signal between the two ultrasonic transducers,

Comparing the simulated flowmeter response to the measured flowmeter response actually received by the receiver circuit, and

• Compute the absolute transit time as the time difference between the simulated flowmeter response and the measured flowmeter response.

Such a method has been shown to be efficient and leads to a very precise determination of the absolute transit time compared to previously known methods.

In an embodiment of the invention, the step of simulating the flowmeter response includes:

providing a single pulse input signal to a signal generator comprising active components to drive the transducer,

monitoring the current from one or more voltage supplies to the active components during or after supplying the input signal to the signal generator to obtain a single pulsed supply current signal for the transducer,

Conditioning the single pulse supply current signal and obtaining a simulated single pulse response of the transducer,

Repeat the previous three steps for the other transducers to obtain another simulated single impulse response,

find the single impulse response of the system by convolving the two obtained single impulse responses of the transducer, and

• Compute the simulated flow meter response by combining multiple instances of the found single impulse response of the system, repeating the above multiple instances with an appropriate delay.

This has been shown to be an efficient way of obtaining a simulated flow meter response that is very similar to the measured flow meter response.

In one embodiment of the invention, the step of simulating the flowmeter response includes:

providing a pulsed input signal to a signal generator comprising active components to drive the transducer,

Obtaining one or more supply current signals by monitoring the current from one or more voltage supplies to active components during or after supplying the input signal to the signal generator,

determining directly from one or more derived supply current signals or from one or more generated signals derived from one or more derived supply current signals, one or more quantities describing the characteristics of the transducer,

Repeat the previous three steps for the other transducers to obtain similar quantities for characterizing the other transducers,

use the determined characteristic quantities of the transducers to find equivalent models of the transducers and build multiple simulation models of the transducers of the flowmeter and the electronic circuits of the signal generator and/or receiver circuits, and

• Simulating the flow meter system by writing a sampled version of the physically transmitted signal to the first transducer or the function of the input signal into a digital simulation model to obtain a simulated flow meter response.

This is another efficient way of obtaining a simulated flow meter response that is very similar to the measured flow meter response.

In an embodiment of the invention, the quantities used to characterize the transducer include an oscillation period and/or a damping parameter determined from at least a portion of one or more obtained and/or derived signals, said The signal portion represents a damped oscillation.

The oscillation period and the damping parameters related to the damped oscillations of the transducer are very useful properties of the transducer which are well suited for constructing a suitable equivalent model of the transducer.

In an embodiment of the invention, one or more Multiple supply current signals.

This is a simple, stable and well known method for measuring current signals.

In an embodiment of the present invention, the step of calculating the absolute transit time includes:

Transform the simulated flowmeter response and the measured flowmeter response into the frequency domain, e.g. by Fast Fourier Transform,

Determining the phase angle between the two flowmeter responses at at least two different frequencies in the frequency domain, and

• Determine the absolute transit time by calculating the group time delay from two determined phase angles.

The use of the Fast Fourier Transform and operation in the frequency domain substantially reduces the amount of computation required to determine the absolute transit time.

In an embodiment of the present invention, the step of calculating the absolute transit time includes:

find the filtered envelopes of the simulated flowmeter response and the measured flowmeter response separately,

Respectively identify two points in time where the filtered envelope reaches 50% of their maximum value, and

• Calculate the absolute transit time as the time difference between two identified points in time.

This method has been shown to provide a very accurate determination of the absolute transit time of the ultrasonic signal through the flow path of the flowmeter.

In one aspect of the invention, it relates to an ultrasonic flowmeter comprising at least one ultrasonic transducer and a signal generator for generating an electrical signal to the transducer, the signal generator comprising active components, wherein the flowmeter Further included is means for measuring one or more supply currents to active components of the signal generator.

This enables the possibility to characterize the transducer when arranging the transducer in the flow meter.

In an embodiment of the invention, the means for measuring the one or more supply currents comprises a resistor inserted in series between the source of the positive supply voltage and the active component.

This is a simple, stable and well known method for measuring current signals.

In an embodiment of the invention, the means for measuring one or more supply currents comprises a resistor inserted in series between the source of the negative supply voltage and the active component.

Measuring the supply current in two supply connections enables faster characterization of the transducer, measuring two supply current signals simultaneously.

In one aspect of the invention, it relates to a method for characterizing an ultrasound transducer, said method comprising the steps of:

providing a pulsed input signal to a signal generator comprising active components to drive the transducer,

Obtaining one or more supply current signals by monitoring the current from one or more voltage supplies to active components during or after supplying the input signal to the signal generator, and

• Determining one or more quantities describing the characteristics of the transducer directly from the one or more obtained supply current signals or from one or more generated signals derived from the one or more obtained supply current signals.

The method enables the characterization of the transducer when it is arranged in the flow meter.

In an embodiment of the invention, the active component is an operational amplifier.

In another embodiment of the invention, the active component is a digital circuit driving the transducer.

This reflects the different types of active components that can be used in a signal generator.

In an embodiment of the invention, one or more Multiple supply current signals.

This is a simple, stable and well known method for measuring current signals.

In an embodiment of the invention, the quantities used to characterize the transducer include an oscillation period and/or a damping coefficient determined from at least a portion of one or more obtained signals and/or derived signals representing damped oscillations.

The oscillation period and the damping parameters related to the damped oscillations of the transducer are very useful properties of the transducer which are well suited for constructing a suitable equivalent model of the transducer.

In an embodiment of the present invention, it relates to a method for determining a time delay of an ultrasonic signal in a flow path of an ultrasonic flowmeter, the method comprising the following steps:

Describe the characteristics of the two transducers of the flowmeter by determining characteristic quantities such as the damping coefficient and the angular frequency of the damped oscillations of the transducers,

find an equivalent model of the transducer using the determined characteristic quantities of the transducer, and build a digital simulation model of the electronic circuit of the transducer, the signal generator of the flowmeter and/or the receiver circuit,

Simulate the flowmeter system by entering into the digital simulation model a functional or sampled version of the input signal of the physically transmitted signal to the first transducer, if not in the transmission of the ultrasonic signal between the two transducers Time delay, then the simulated model response corresponding to the output signal from the receiver circuit according to the model is thus obtained,

record the physical flowmeter response actually received by the receiver circuit, and

• Calculate the absolute transit time by determining the time delay of the physical flowmeter response compared to the simulated model response.

This method has been shown to provide a very accurate determination of the absolute transit time of the ultrasonic signal through the flow path of the flowmeter.

In an embodiment of the present invention, the step of calculating the absolute transit time includes the following steps:

find the filtered envelopes of the simulated model response and the physical flowmeter response separately,

Respectively identify two points in time where the filtered envelope reaches 50% of their maximum value, and

• Calculate the absolute transit time as the time difference between two identified points in time.

This method of calculating absolute transit times has been shown to be very accurate and reproducible, considering that transducer parameters are very likely to vary not only between samples, but also as temperature changes and over time.

In one aspect of the invention, it relates to an ultrasonic flowmeter comprising at least one ultrasonic transducer and a signal processing unit for processing electrical signals received from the at least one ultrasonic transducer, wherein the signal processing unit is arranged to A sampling frequency lower than twice the resonance frequency of the at least one ultrasound transducer digitizes the continuous signal.

This allows slower and cheaper analog-to-digital converters to be used in the flowmeter than would otherwise be required.

In one aspect of the present invention, it relates to an ultrasonic flowmeter comprising a flow path for fluid flow; at least two ultrasonic transducers acoustically coupled to the flow path, wherein one transducer is arranged along the flow path at upstream of another transducer; a signal generator for generating an electrical transmit signal to the transducer, the signal generator including a negative feedback coupled operational amplifier; a receiver circuit for receiving an electrical receive signal from the transducer , the receiver circuit includes a negative feedback coupled operational amplifier; a switching unit for switching the electrical transmission signal between the signal generator and the transducer, and for switching the electrical reception signal between the transducer and the receiver circuit; the signal a processing unit for providing an output indication of the flow rate on the flow path from the electrical receive signal, wherein the switching unit is coupled to the output of the operational amplifier of the signal generator and the switching unit is coupled to the inverting input of the operational amplifier of the receiver circuit .

Thus, the present invention particularly relates to high precision, high capacity, low power and low cost consumption meters for billing purposes.

By coupling the switching unit and the transducer with the output of the operational amplifier of the signal generator and with the inverting input of the operational amplifier of the receiver circuit, it is achieved that the impedance seen from the transducer is the same regardless of the transduced The transmitter can operate as a transmitter or as a receiver. This means that the reciprocity theorem for linear passive circuits applies to the flowmeter, which is important for its stability and manufacturability.

In an embodiment of the present invention, compared to the impedance of the transducer, the output impedance of the signal generator and the input impedance of the receiver circuit are negligible, such as less than 10 ohms, preferably less than 1 ohm, more preferably less than 0.1 ohms.

Choosing a very low output impedance of the signal generator SG and a very low input impedance of the receiver circuit RC is advantageous to obtain that the transducers will experience both transducers in sufficient proximity to each other and to ensure minimal attenuation of the electrical transmitted and received signals.

In an embodiment of the invention, the signal generator and receiver circuits share at least one active component.

This helps save component costs when producing flow meters.

In an embodiment of the invention, all active components of the signal generator are completely isolated from all active components of the receiver circuit.

Using different active components for the signal generator and receiver circuits makes it possible to transmit the signal all the way through the flow meter without any switching of the transmission path during transmission.

In an embodiment of the invention, one or more operational amplifiers in the signal generator and receiver circuit are current feedback operational amplifiers.

The use of current feedback amplifiers is advantageous due to their lower input impedance at the inverting input, greater bandwidth and lower power consumption than other types of op amps and Higher gain at high frequencies.

In an embodiment of the invention, one or more operational amplifiers in the signal generator and receiver circuits operate with an input common mode voltage whose AC component is substantially zero or at least negligible.

This is important for some types of op amps, especially the fastest op amps with the highest bandwidth and very low current consumption, because the allowable voltage swing on the input for linear operation can be sufficiently limited.

In an embodiment of the invention at least two transducers are arranged to be able to transmit ultrasound signals simultaneously.

In this configuration, the electrical transmission signal is sent only half as often as in other configurations in order to conserve battery life. Furthermore, the time of flight is measured simultaneously in both directions, and thus no sudden change in flow velocity occurs between measurements in the two directions.

Description of drawings

In the following, some exemplary embodiments of the present invention are described and explained in more detail with reference to the accompanying drawings, in which

Fig. 1 schematically describes the overall structure of an ultrasonic flowmeter known in the prior art for transit time flow measurement;

Figure 2a schematically depicts the coupling of an ultrasonic transducer in an ultrasonic flowmeter known in the prior art;

Figure 2b schematically depicts the coupling of an ultrasonic transducer in another ultrasonic flowmeter known in the prior art;

Fig. 3 has schematically described the coupling of the ultrasonic transducer in the ultrasonic flow meter according to the embodiment of the present invention;

Fig. 4 has schematically described the coupling of the ultrasonic transducer in the ultrasonic flow meter according to another embodiment of the present invention;

Fig. 5 has schematically described the coupling of the ultrasonic transducer in the ultrasonic flow meter according to another embodiment of the present invention;

Figure 6 shows a schematic diagram of the most basic electronic components in an ultrasonic flowmeter according to an embodiment of the present invention;

Fig. 7 a schematically depicts the structure for performing the first step to obtain the power supply current signal for driving the active components of the ultrasonic transducer;

Fig. 7 b schematically describes the structure for performing the second step to obtain the power supply current signal of the active components driving the ultrasonic transducer;

Figure 7c describes a preferred way of connecting the signal generator and receiver circuits for obtaining such a power circuit signal;

Figure 8a schematically depicts a first step in obtaining the characteristics of an ultrasonic transducer from a supply current signal driving the active components of the ultrasonic transducer;

Figure 8b schematically describes the second step of obtaining the characteristics of the ultrasonic transducer from the supply current signal driving the active components of the ultrasonic transducer;

Figure 9 depicts a known equivalent diagram of an ultrasonic transducer;

Figure 10 describes some steps in deriving a simple equivalent diagram of an ultrasonic flowmeter according to the invention;

Figure 11 depicts the differences and similarities between the physical and simulated signal chains through a flow meter according to the present invention;

Fig. 12 schematically depicts a method for very accurately determining the time delay of an ultrasonic signal on a flow path according to the present invention;

Figure 13 schematically describes in more detail a method of calculating an absolute transit time from a response signal obtained by a method like that described in Figure 12;

Figure 14 depicts an equivalent diagram of a signal generator according to the present invention and an ultrasonic transducer connected thereto;

Figure 15a depicts a single pulse signal;

Figure 15b depicts the power supply current signal obtained by the first ultrasonic transducer in response to the single pulse in Figure 15a;

Figure 15c depicts the supply current signal obtained by the second ultrasonic transducer in response to the single pulse in Figure 15a;

Figure 15d depicts the supply current signal obtained without any ultrasonic transducer in response to the single pulse in Figure 15a;

Figure 16a depicts the calculated single impulse response of the first ultrasound transducer;

Figure 16b depicts the calculated single impulse response of the second ultrasonic transducer;

Figure 16c depicts the calculated single impulse response of the entire ultrasonic transducer system according to the present invention;

Figure 17a depicts the simulated flowmeter response;

Figure 17b depicts the measured flowmeter response;

Figure 18a depicts the theoretical relationship between the magnitude of real and simulated flowmeter responses in the frequency domain;

Figure 18b depicts the theoretical phase angles of the real and simulated flowmeter responses in the frequency domain;

Figure 19 depicts an example of the corresponding simulated and measured flowmeter responses;

Figure 20a depicts the magnitude in the frequency domain of the simulated flowmeter response shown in Figure 19;

Figure 20b depicts the magnitude of the measured flowmeter response shown in Figure 19 in the frequency domain;

Figure 21a depicts the actual phase angle between the flowmeter responses shown in Figure 19;

Figure 21b depicts a portion of the graph shown in Figure 21a;

Figure 22 depicts the slope of the portion shown in Figure 21b;

Figure 23a depicts an example of a spectrum of a continuous signal;

Figure 23b schematically depicts the spectral sequence of undersampling a continuous signal, the spectrum of which is depicted in Figure 23a;

Figure 23c schematically depicts how an undersampled signal can be reconstructed by varying the sampling frequency and filtering the signal;

Figure 24a depicts an embodiment of a continuous signal;

Figure 24b depicts the digital samples obtained by sampling the signal of Figure 24a at a sampling frequency of 5/6 of the signal frequency;

Figure 25a depicts the reconstruction of the signal of Figure 24a using a broadband FIR reconstruction filter;

Figure 25b depicts the reconstruction of the same signal using a narrowband FIR reconstruction filter;

Figure 26 schematically depicts a method for finding the magnitude and phase of an undersampled continuous signal;

Figure 27 schematically depicts a method for reconstructing an undersampled continuous signal without distortion;

FIG. 28 schematically depicts an expanded method according to the invention for very precise determination of the time delay of ultrasound signals in a flow path.

Detailed ways

FIG. 1 shows the general structure of an ultrasonic flowmeter known in the prior art for transit-time flowmetering. The controller unit CU controls the operation of the signal generator SG, the switching unit SU and the receiver circuit RC, where the switching unit SU is on one side the signal generator SG and the receiver circuit RC with the two ultrasonic transducers on the other side. Different electrical connections are established between the transducers TR1 and TR2. Two transducers TR1 , TR2 are arranged in the flow path FP in which the fluid flow is to be metered, one transducer TR1 upstream of the other transducer TR2 along the flow path FP.

In principle, flow metering is performed in three steps:

1. The switch unit SU is established to connect the signal generator SG to the first transducer TR1 and to connect the second transducer TR2 to the receiver circuit RC.

An electrical transmission signal (typically a pulsating signal with a frequency of several megahertz and a duration of several microseconds) is sent from the signal generator SG through the switching unit SU to the first transducer TR1 from which the signal Transmitted as an ultrasonic signal through the fluid to the second transducer TR2. From TR2, the signal continues as a current reception signal through the switching unit SU to the receiver circuit RC, where the reception signal is converted into a voltage signal.

The signal processing unit (part of the controller unit CU in the configuration shown in Fig. 1), analyzes the voltage signal, from transducer TR1 to transducer TR2, by the delay of the electrical received signal compared to the electrically transmitted signal, and calculates The transit time of the ultrasonic signal through the fluid is recorded and recorded (t ₁ ).

2. Change the configuration of the switching unit SU to connect the signal generator SG with the second transducer TR2 and the first transducer TR1 with the receiver circuit RC.

As in step 1, the electrical transmission signal is sent from the signal generator SG, and the electrical reception signal is received by the receiver circuit RC, only this time the ultrasonic signal is transmitted through the fluid in the opposite direction, that is, from the second transducer TR2 to the first transducer TR1.

Again, the signal processing unit calculates and records the transit time (t ₂ ).

3. The signal processing unit calculates an indication of the flow on the flow path FP with a formula of the form:

$\mathrm{\&Phi;}\&Proportional;K(t_1-{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">t</figure-callout>}}_2,{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">t</figure-callout>}}_1+t_2)\&Center\; Dot;\frac{t_1-t_2}{{({\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">t</figure-callout>}}_1+t_2)}^2}$ (Formula 1)

where Φ is a flow indicator proportional to the fraction shown in Equation 1 multiplied by the correction factor K found in the correction factor table, which once determined will be used for all flowmeters of a given type for a given fluid.

This table of correction factors takes into account physical quantities such as the size and physical configuration of the flow path FP in the flowmeter and fluid viscosity.

As can be seen from Equation 1, once the correction factor table is established, the flow indication can be calculated from the two quantities (t ₁ -t ₂ ) and (t ₁ +t ₂ ).

The first of these quantities, (t ₁ -t ₂ ), which is the difference between the two transit times, is typically on the order of a few nanoseconds, but can be obtained by finding the phase difference between the two received signals to easily determine. It can be done very precisely (up to 10-100 picoseconds) by several analog and digital methods known over the years, due to the fact that, assuming the application of the reciprocal law for linear passive circuits, Due to the different transit times (t ₁ and t ₂ ), the two received signals are identical except for the phase difference. In general, this is the case if it is ensured that the impedance (as seen from the transducers TR1 , TR2 ) is the same whether the transducers TR1 , TR2 act as transmitters or receivers of ultrasound waves.

On the other hand, it is difficult to calculate exactly another quantity, (t ₁ +t ₂ ), which is the sum of two transit times, typically on the order of a few microseconds, because it includes the exact transit time The calculation of (t ₁ and t ₂ ), which again requires very precise determination of the leading edge of each received signal, is by no means a simple task due to the shape of the received signal.

Therefore, in many known flow meters, this quantity is not actually counted. Instead, estimate using the following formula:

$\frac{d}{c}=t\&ap;{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">t</figure-callout>}}_1\&ap;t_2$ (Formula 2)

In this formula, d is the distance between the two transducers TR1 , TR2 and c is the velocity of ultrasonic waves in the actual fluid whose flow rate is being metered. For a given flow meter, d is obtained from the physical position of the transducers TR1, TR2 on the flow path FP and, for a given temperature, the velocity of ultrasound in the given fluid can be found in the table. Thus, by measuring the temperature of the fluid, an estimate of t ₁ and t ₂ can be found, which can then be used to estimate the quantity (t ₁ +t ₂ ) used in Equation 1 .

Figures 2a and 2b schematically depict embodiments of the coupling of ultrasonic transducers in ultrasonic flowmeters according to the inventions of Tonnes (EP 0846936) and Jespersen (EP 1438551), respectively.

Properly implemented, both couplings ensure that the reciprocal laws for linear passive circuits apply.

In the coupling shown in Fig. 2a, the electrical transmission signal is transferred from the signal generator SG to the transducer TR1 through the signal impedance Zsig. In the coupling shown in Fig. 2b, on the other hand, the signal generator SG comprises a negative feedback coupled amplifier circuit in which the digital pulse signal is connected to the non-inverting input of the operational amplifier OPsg, and the signal impedance Zsig forms the Feedback between output and inverting input. The transducer TR1 is connected to the inverting input of the operational amplifier OPsg via an adaptive impedance Zad, which is much smaller than the signal impedance Zsig and is therefore practically negligible.

In the two illustrated couplings, the switching unit SU comprises two switches SW1, SW2 arranged to be able to connect the two transducers TR1, TR2 respectively with a common conductor CC connecting the signal generator SG with Receiver circuit RC connection. In both cases, the position of each of the switches SW1, SW2 needs to be changed in flow metering in order to ensure that when the electrical transmission signal is transmitted from the signal generator SG, one of the transducers TR1, TR2 is connected to the common conductor CC connected, whereas the other transducer TR2, TR1 is connected with the common conductor CC when the electrical receive signal is received by the receiver circuit RC. This change of switch position has to take place after the ultrasound signal has left the transmitting transducer TR1, TR2, but before it reaches the receiving transducer TR2, TR1. Therefore, timing is very important.

In the two couplings shown in Fig. 2a and Fig. 2b, the signal impedance Zsig through which the signal current passes has the function of converting the current signal received from the transducers TR2, TR1 into a measurable voltage signal. The magnitude of the voltage signal is found by multiplying the received current by the signal impedance Zsig, a larger signal impedance Zsig results in a larger received voltage signal.

Unfortunately, due to the practical limitation of the supply voltage provided to the signal generator SG, the signal impedance Zsig also limits the electrical signal that can be provided to the transducers TR1, TR2 due to the There is also a signal impedance Zsig. Therefore, the output voltage from the signal generator SG must be greater than the signal required on the transducers TR1, TR2. The compromise that results in a maximum received voltage signal is that the value of the signal impedance Zsig ranges between 0.5 and 2 times the impedance of the ultrasound transducers TR1 , TR2 at the frequency of interest.

In another aspect, the present invention provides a stable, producible flow meter capable of transmitting high acoustic signals while amplifying received current signals with high signal impedance and low impedance at sensitive nodes in the circuit.

The basic idea of the invention is to connect the transducers TR1, TR2 with different nodes in the transmit and receive situations, to ensure that the reciprocity law for linear passive circuits still applies, that is, without sacrificing the property that whether or not The transducers TR1, TR2 are used as transmitters or receivers, the impedance seen from the transducers TR1, TR2 is the same.

This is achieved by coupling the switches SW1, SW2 of the switching unit SU with the output of the operational amplifier OPsg of the signal generator SG and the switching input of the operational amplifier OPrc of the receiver circuit RC, as shown in the diagram illustrating an embodiment of the invention 3 for a schematic description.

By using an operational amplifier OPsg with a very low output impedance in the signal generator SG and by selecting the feedback components leading to a suitable feedback impedance Zfb, sg, Zfb, rc for the two operational amplifiers OPsg, OPrc respectively to build a negative feedback circuit , a signal generator SG with very low output impedance and a receiver circuit RC with very low input impedance can be obtained, while illustrating the parasitic components of the operational amplifiers OPsg, OPrc. Very low impedance can be obtained by coupling an op amp with high gain at the frequency of interest with negative feedback.

It is advantageous to choose a very low output impedance of the signal generator SG and a very low input impedance of the receiver circuit RC for four reasons:

First, if these impedances are sufficiently low compared to the impedances of both transducers TR1, TR2 and account for parasitic components, then even between the output impedance of the signal generator SG and the input impedance of the receiver circuit RC In practice there may be a slight difference, and the transducers TR1, TR2 will also consider the two impedances to be close enough to each other. In practice, this means that the reciprocal laws for linear passive circuits apply and the flowmeter is stable and producible.

For a proper implementation, the output impedance of the signal generator SG and the input impedance of the receiver circuit RC should both be negligible compared to these transducer impedances, that is, less than 1% of the transducer impedance, preferably less than 0.1% of transducer impedance. The transducer impedance at the frequency of interest typically falls within the range of 100 ohms - 1000 ohms, depending on transducer size and material and the frequency of the transmitted signal.

Second, the choice of small output and input impedances ensures that attenuation of the electrical transmitted and received signals is minimized, maximizing the output signal received by the receiver circuit RC.

Third, a very low impedance is chosen, since it is difficult to match mid-range values within negligible tolerances in different parts of the circuit, especially complex impedances and where more than absolute impedance values are to be considered.

Fourth, the low circuit impedance is less susceptible to interference from external noise sources.

A clear advantage of the coupling shown in Fig. 3 is that by using two different operational amplifiers OPsg, OPrc in the signal generator SG and the receiver circuit RC respectively, between the two transducers TR1, TR2, in the ultrasonic signal No switching between transmission and reception is required. When the switches SW1 and SW2 are in the positions shown in Figure 3, the electrical transmission signal will be transmitted from the signal generator SG to the second transducer TR2 through the second switch SW2, and the ultrasonic signal will be transmitted by the second transducer TR2 through the flow path ( FP) to the first transducer TR1, so that the electrical reception signal will reach the receiver circuit RC from the first transducer TR1 through the first switch SW1. In order to transmit the ultrasonic signal in the opposite direction, the positions of the two switches SW1, SW2 have to be reversed and again the signal is transmitted from the signal generator SG all the way to the receiver circuit RC without any switching during transmission. In this way, switching noise is avoided and more accurate metering can be performed.

It is known in the prior art that separate circuits have been used to construct the signal generator and receiver circuits. However, in these cases, either the transducers experience different impedances in the transmit and receive situations, or the amplification factors for the two transducers are different, the invention does not adequately disclose beyond the theoretical, or the choice of high impedance.

The latter has the disadvantage that it is very challenging to design a signal generator whose output impedance is much larger (100-1000 times) than the transducer impedance at frequencies of interest (100kHz to 10MHz). It also has the disadvantage that optimization of the output signal amplitude needs to take into account the transducer impedance used to obtain the optimized signal level. This is not trivial since the impedance of an ultrasound transducer depends mostly on the temperature and the difference between samples. Last, but not least, such methods are more sensitive to electrical noise.

In recent years, new operational amplifiers have been designed with very low impedance that are feasible, even in battery powered flow meters. In particular, so-called current-feedback op amps, which have low input impedance at the inverting input and also have higher bandwidth at high frequencies, lower power consumption and Higher gains are beneficial for use in the present invention.

Fig. 4 schematically depicts the coupling of an ultrasonic transducer in an ultrasonic flow meter according to another embodiment of the invention, wherein the same circuit is used in the signal generator SG and the receiver circuit RC. A significant advantage of the present invention is that there is only one common operational amplifier OP, and therefore only one set of feedback components is required to provide the desired resulting feedback impedance Zfb.

Since the signal path needs to be switched during signal transmission, the price used to cover this cost is saved. As shown in Fig. 4, each of the two switches SW1, SW2 connecting the two transducers TR1, TR2 with the combined signal generator and receiver circuit SG/RC has three possible positions each.

This means that each of the two transducers TR1, TR2 is able to:

1. By coupling with the output of the operational amplifier OP in order to set the transducer to transmit the ultrasonic signal, receive the electrical transmission signal from the operational amplifier OP, and the public circuit SG/RC as a signal generator,

2. By coupling with the reverse input terminal of the operational amplifier OP so as to set the transducer to receive the ultrasonic signal, the electric receiving signal is transmitted to the operational amplifier OP, and the public circuit SG/RC is used as the receiving circuit, or

3. When other transducers are connected to the common circuit, disconnect the common circuit SG/RC.

Therefore, by appropriately setting and changing the positions of the switches SW1, SW2 at an appropriate time, desired signal paths of the electrical transmission signal, the ultrasonic signal and the electrical reception signal can be obtained. For the transmission of ultrasonic signals from the first transducer TR1 to the second transducer TR2, the first transducer is first set up by connecting the first transducer TR1 with the common circuit SG/RC working as a signal generator TR1 transmits ultrasound signals, while the second transducer TR2 is disconnected from the common circuit SG/RC. Subsequently, when the ultrasonic signal is transmitted by the first transducer TR1 but before it reaches the second transducer TR2, the first transducer TR1 is disconnected from the common circuit SG/RC, and by connecting the second transducer TR2 is connected to the common circuit SG/RC operating as a receiver circuit, and the second transducer TR2 is arranged to receive ultrasonic signals. For transmitting ultrasound signals in the opposite direction, the connection of the two transducers TR1 , TR2 is simply swapped compared to the above description.

Fig. 5 schematically depicts the coupling of an ultrasonic transducer in an ultrasonic flowmeter according to another embodiment of the present invention. In this case there are two receiver circuits RC1, RC2, each comprising an operational amplifier OPrc1, OPrc2 and a negative feedback circuit with impedances Zfb, rc1 and Ffb, rc2, respectively. This allows both transducers TR1, TR2 to transmit ultrasound signals simultaneously.

To do this, both transducers TR1 , TR2 are firstly connected to the signal generator SG by setting the switches SW1 , SW2 at suitable positions. The electrical transmission signal is transmitted simultaneously to two transducers TR1, TR2 from which said signal is transmitted into the flow path (FP) as a signal from each transducer TR1, TR2 the ultrasonic signal. Before the ultrasonic signal from the first transducer TR1 reaches the second transducer TR2, and vice versa, the position of the switches SW1, SW2 is changed so that each of the transducers TR1, TR2 is connected to the receiver circuit RC1, RC2 A connection in .

In this way, ultrasonic signals can be sent upstream and downstream along the flow path FP in a single operation. However, in order to eliminate any possible minor metering errors, it should be ensured that for each transmission of the ultrasonic signal the connections between the transducers TR1, TR2 and the receiver circuits RC1, RC2 are interchanged so that at each second time, A given transducer TR1 , TR2 is only connected to the same receiver circuit RC1 , RC2 , where the metering error is due to the fact that the two receiver circuits RC1 , RC2 cannot be constructed identically.

Another difference between the coupling shown in the preceding figures and the coupling shown in FIG. 5 is that the digital pulse signal is connected to the inverting input of the operational amplifier OPsg of the signal generator SG via a filter impedance Zfilt, wherein the filter impedance Zfilt affects the amplification and filtering of the electrical transmission signal, and the non-inverting input of the operational amplifier OPsg is grounded.

Compared to the configuration of the signal generator SG shown in the previous figures, where the input common mode voltage of the operational amplifier exhibits some variation as the digital ripple signal varies, this configuration has the input common mode voltage held constant The advantage of the DC level. This is important for some types of op amps, especially the fastest op amps with the highest bandwidth.

Fig. 6 shows a schematic diagram of the most basic electronic components in an ultrasonic flow meter according to an embodiment of the present invention.

In this figure, the two inputs labeled IN1 and IN2 indicate the inputs of the two digital pulse signals, the two resistors R4 and R7 are used to generate a symmetrical transmission signal for the signal generator SG through the two digital signals, and the capacitor C7 An AC coupling is formed between the incoming transmission signal and the signal generator SG.

The two resistors R3 and R9 and the two capacitors C1 and C9 form a low-pass filter (corresponding to Zfilt in Figure 5) for the incoming transmission signal.

OPsg is the operational amplifier of the signal generator SG, which not only amplifies the incoming transmission signal, but is also important for adjusting the output impedance of the signal generator SG to be very low (ie practically 0).

The three resistors R1, R2 and R40 and the two capacitors C29 and C30 jointly constitute the negative feedback impedance of the operational amplifier OPsg (corresponding to Zfb and sg in Figure 3 and Figure 5).

The three resistors R11 , R41 and R45 together form a voltage divider that defines the reference voltage for the inverting inputs of OPsg and OPrc. Since both OPsg and OPrc are configured as inverting amplifiers, the reference voltage is the same as the input common mode voltage on the two operational amplifiers OPsg and OPrc respectively. The reference voltage supplied to the two operational amplifiers OPsg and OPrc is decoupled by two capacitors C2 and C25.

V3 (corresponding to VCC in Figure 7a and Figure 7b) is the positive supply voltage for the circuit. In low power flowmeters (eg battery powered flowmeters), V3 may preferably be turned off by a switch (not shown in the figure) most of the time so that the circuit operates at a very low duty cycle.

In the embodiment shown in Fig. 6, the switching unit SU comprises four switches implemented on a single CMOS chip in an integrated circuit for coupling the transducers TR1, TR2 with the signal generator SG and the receiver circuit RC. By maintaining a high voltage, each of the pins IN1-IN4 of the switching unit SU controls one of the four switches connected between the lines D1-S1, D2-S2, D3-S3 and D4-S4 respectively. In the diagram shown in Figure 6, the switch is configured to pass a signal from transducer TR1 to transducer TR2. For the signal to be transmitted from transducer TR2 to transducer TR1, opposite voltages must be applied to IN1-IN4. Preferably, IN1-IN4 are controlled by a microcontroller.

The two resistors R10 and R36 are small current limiting resistors. The stability of the operational amplifiers OPsg, OPrc can be increased by limiting the capacitive loading on the amplifiers OPsg, OPrc.

Two capacitors C8 and C15 provide AC coupling of the signal to and from the transducers TR1, TR2. This allows the use of operational amplifiers OPsg, OPrc of a single supply voltage, such as the one shown in Fig. 6, without any DC voltage on the transducers TR1, TR2.

The two resistors R13 and R14 are voltage dividers (bleeders) for discharging the charges on the transducers TR1 , TR2 in case charges are generated on the transducers TR1 , TR2 due to pyroelectric effects or due to other circumstances.

Preferably, the two ultrasonic transducers TR1 and TR2 consist of thermoelectric transducers.

OPrc is the operational amplifier of the receiver signal RC, which produces an amplified output signal OUT from the electrical receive signal from the transducers TR1, TR2, and is useful for adjusting the input impedance of the receiver circuit RC to be very low (i.e., practically to 0) is important.

Resistor R44 and capacitor C5 form a filter of the supply voltage for the operational amplifier OPrc of the receiver circuit RC.

The two resistors R5, R6 and capacitor C4 together form the negative feedback impedance of the operational amplifier OPrc (corresponding to Zfb, rc in Figure 3).

Two resistors R8 (corresponding to RCC in Figures 7a and 7b) and R43 are used for current sensing of the supply current to the operational amplifier OPsg. In some embodiments of the invention, R43 may be omitted for increased stability. If the OPsg is chosen to be an operational amplifier with a low supply voltage rejection ratio, a switch (not shown in the figure) is required to short R8 and R43 during the transit time measurement.

The two capacitors C6 and C33 have the purpose of decoupling the supply voltage from OPsg. If the values of these two capacitors are too high, the voltage across R8 and R43 will not correctly reflect the supply current to the operational amplifier OPsg. On the other hand, if the values of C6 and C33 are too low, the operational amplifier OPsg may be unstable.

The two capacitors C13 and C14 and the two resistors R12 and R15 are the components required to combine the two supply currents SCSa, SCSb into a single signal (supply current signal SCS). R12 and R15 also define the DC voltage level for the compliance flowmeter circuit (eg, analog to digital converter).

V1 is the supply voltage required to generate the DC voltage level for the combining circuits C13, C14, R12, R15. Through careful selection of components, V3 can be reused instead of a separate supply voltage V1.

Figures 7a and 7b schematically depict structures for performing the first and second steps respectively to obtain the supply current signals SCS-, SCS+ for driving the active components of the ultrasonic transducer.

In the first step as shown in Fig. 7a, the first short digital pulse input signal DSPa is used as the input of the signal generator SG driving the ultrasonic transducers TR1, TR2, which can be connected with the ultrasonic transducers through the switching unit SU TR1, TR2 connection. The signal generator SG may comprise a negative feedback coupled operational amplifier (OP; OPsg), as shown in the preceding figures, or it may comprise another active component capable of amplifying the input signal DPSa and providing the output impedance of the signal generator SG, Wherein the output impedance is very low, that is, substantially zero. For example, the active components may consist of digital circuits that drive transducers.

A current sensing resistor RCC (corresponding to R8 in FIG. 6 ) is arranged in series between the active component of the signal generator SG and the positive voltage supply VCC (corresponding to V3 in FIG. 6 ) for this active component. Now, by monitoring the voltage across this current sensing resistor RCC, a first supply current signal SCSa representing the current supplied to the active components from the positive voltage supply can be obtained, as shown on the right side of Fig. 7a.

It should be noted that when the input signal DPSa stops oscillating, the transducer will continue to oscillate for some time, still drawing some current from the positive voltage supply through the active components. This is manifested in the first supply current signal SCSa, which comprises a greater number of oscillations compared to the first input signal DSPa, as shown in Figure 7a, the latest part of the signal DSPa showing the self-oscillating transduction The registers TR1, TR2 perform damped oscillations.

It can also be seen from the first supply current signal SCSa shown in FIG. The value is 0. This is due to the fact that if the active components of the signal generator are coupled with non-inverting amplifiers, the positive voltage supply VCC only delivers current to the active components when the voltage of the input signal DPSa is higher than the input common mode voltage of the active components. source components, and if the active components are coupled with an inverting amplifier, the positive voltage supply VCC only delivers current to the active components when the voltage of the input signal DPSa is lower than the input common mode voltage of the active components.

Therefore, to obtain the second supply current signal SCSb comprising the other half of each oscillation, the measurement is repeated with another digitally pulsed input signal DPSb which is identical to the first input signal DPSa except that the signal polarity is reversed. turn outside.

It should be noted that if a similar current sense resistor (not shown in Figures 7a and 7b, but corresponding to R43 in Figure 6) is arranged in series between the active components and the negative voltage supply for the active components ( When not shown in the figure), two supply current signals SCSa, SCSb can be simultaneously obtained from the positive voltage supply and the negative voltage supply of the active components of the signal generator SG respectively.

Fig. 7c describes a preferred way of connecting the signal generator SG and the receiver circuit RC for obtaining such supply current signals SCSa, SCSb.

In this case, the active components OPrc of the receiver circuit RC serve to amplify the supply current signals SCSa, SCSb. The connection between the signal generator SG and the receiver circuit RC comprises a switch SWconn connected in series and a high-pass filter formed by a capacitor Cconn and a resistor Rconn.

Since the connections SWconn, Cconn, Rconn are connected at the inverting input of the active component OPrc of the receiver circuit RC to the summation point, the supply current signals SCSa, SCSb do not in any way affect the ultrasonic transducers TR1, Function of TR2.

Furthermore, due to the transit time of the ultrasonic signal between the two transducers TR1, TR2 on the flow path FP, the supply current signals SCSa, SCSb and the signal transmitted between the transducers TR1, TR2 will be at different times to the receiver circuit RC.

At high frequencies, component non-idealities potentially affect the signal, and the supply current signals SCSa, SCSb can affect the signal received through the flow path FP and vice versa. A remedy for minimizing this effect is to measure the supply current signals SCSa, SCSb and the ultrasonic signal at different times and to disconnect the unused circuit parts from the input of the active component OPrc of the receiving circuit RC via the switches SW2, SWconn .

If the signal generator SG is configured as a class A amplifier, the current into the positive voltage supply pin is essentially constant, and a current sense resistor (R43) needs to be placed in series with the negative voltage supply for a useful signal.

As shown in Fig. 8a, by subtracting the two supply current signals SCSa, SCSb from each other, the subtraction supply current signal SCS- is obtained, and from the subtraction supply current signal SCS-, by measuring two suitable values of the selected signal SCS- The time difference between the zero crossings of , also shown in FIG. 8 a , can easily determine the oscillation period Tscs of the damped oscillation of the transducers TR1, TR2.

The relationship between the oscillation period Tscs and the frequency fD of the damped transducer oscillation and the angular frequency _ωD is known:

$\mathrm{Tscs}=\frac{1}{f_{\mathrm{D.}}}=\frac{1}{2\mathrm{\&pi;}{\mathrm{\&omega;}}_{\mathrm{D.}}}$ (Formula 3)

Furthermore, by adding the two supply current signals SCSa, SCSb to each other, as shown in Fig. 8b, the summed supply current signal SCS+ can be obtained, so that the envelope Escs of its attenuation part can be determined. This envelope Escs has the shape of an exponential curve with respect to time t, and the mathematical formula describing the envelope is

Escs＝-ke- ^αt (Formula 4)

where k is a constant and α is the damping parameter of the damped oscillation of the transducers TR1, TR2.

In principle, ω _D and α can be found separately from each measured supply current signal SCSa, SCSb. However, these two quantities can be determined more accurately by using the subtracted supply current signal SCS- and the added supply current signal SCS+ as shown in Figures 8a and 8b.

These two quantities ω _D and α are very useful for describing the characteristics of the transducer, indicating the condition of the transducer (for example, whether it is damaged or whether there may be air around the transducer, assuming it is surrounded by water, etc.) useful.

Fig. 9 depicts a known equivalent diagram of an ultrasound transducer TR comprising a parallel capacitance Cpar coupled in parallel with a series connection of a series inductance Lser, a series capacitance Cser and a series resistance Rser.

Figure 10 describes some steps in deriving a simple equivalent diagram of an ultrasonic flowmeter, which can be used to simulate a signal chain with a flowmeter according to the invention.

The equivalent diagram in the first part of Figure 10 describes how a flow meter can be equivalent by a system comprising two ultrasonic transducers TR1, TR2, where the first transducer of the transmission signal in the form of a voltage signal Vtr1 is applied TR1 sends the ultrasonic signal to the second transducer TR2, which thereby generates a received signal in the form of a current signal Itr2.

For a given input signal to the signal generator of the flow meter, the voltage signal Vtr1 applied to the first transducer TR1 is the same for each time-of-flight measurement, since all components of the signal generator for Every measurement is the same. This also means that the applied signal Vtr1 can be calculated from the input signal by using the filter mode of the signal generator, as soon as this filter mode is determined once or all, or it can be recorded by an analog-to-digital converter, before the simulation process, This is described below.

The equivalent diagram for each of the two transducers TR1, TR2 in the equivalent diagram of the flowmeter shown in the first part of FIG. 10 is introduced from FIG. 9, resulting in the second part of FIG. 10 The schematic diagram shown. Here, it should be noted that due to the fact that the ultrasonic signal transmitted by the first transducer TR1 is proportional to the current signal Itr1 passing through the transducer TR1, the voltage signal Vtr2 applied to the transducer TR2 can equivalently reach the first The ultrasonic signal of the second transducer TR2 is proportional to the voltage signal Vtr2 and the current signal Itr1 through the proportional factor K1, as shown in FIG. 10 .

In the equivalent diagram of the second part of FIG. 10 , the parallel capacitances Cpar1 , Cpar2 have no effect on the applied voltage Vtr1 , Vtr2 across the serially connected Lser1 , Cser1 , Rser1 and Lser2 , Cser2 , Rser2 respectively, and can therefore be ignored. Accordingly, the corresponding equivalent diagrams for a flowmeter for simulating the signal chain through the flowmeter are the equivalent diagrams described in the third and fourth parts of FIG. 10 .

The relationship between the applied voltage signals Vtr1, Vtr2 and the generated current signals Itr1, Itr2 can be obtained by the known differential formula:

$\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="Itr"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">Itr</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="Vtr"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">Vtr</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="sLser"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">sLser</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="sCser"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">sCser</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="Rser"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">Rser</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}}$

$=\frac{1}{\mathrm{<figure-callout\; id="1"\; label="lser"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">lser</figure-callout>}1}\frac{\mathrm{the\; s}}{{\mathrm{the\; <figure-callout\; id="2"\; label="s"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">s</figure-callout>}}^2+\mathrm{the\; <figure-callout\; id="1"\; label="s\; Rser"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">s</figure-callout>}\frac{\mathrm{Rser}}{}\frac{1}{\mathrm{<figure-callout\; id="1"\; label="lser"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">lser</figure-callout>}1}+\frac{1}{\mathrm{<figure-callout\; id="1"\; label="lser"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">lser</figure-callout>}1\mathrm{<figure-callout\; id="1"\; label="Cser"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">Cser</figure-callout>}1}}\mathrm{Vtr}1$ (Formula 5)

$\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="Itr"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">Itr</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="Vtr"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">Vtr</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="sLser"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">sLser</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="sCser"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">sCser</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="Rser"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">Rser</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}}$

$<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="K"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">K</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="Vtr"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">Vtr</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="sLser"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">sLser</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="sCser"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">sCser</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="Rser"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">Rser</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}}$

$<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="K"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">K</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="lser"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">lser</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="lser"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">lser</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}}\frac{\mathrm{<span\; class="notranslate">\; the\; s</span>}}{{\mathrm{<span\; class="notranslate">\; the\; <figure-callout\; id="2"\; label="s"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">s</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; the\; <figure-callout\; id="1"\; label="s\; Rser"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">s</figure-callout></span><figure-callout\; id="1"\; label="s\; Rser"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">\; </figure-callout>}\frac{\mathrm{<span\; class="notranslate">\; </span>}}{}\frac{\mathrm{<span\; class="notranslate">Rser</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="lser"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">lser</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="lser"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">lser</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="Cser"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">Cser</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}\frac{\mathrm{<span\; class="notranslate">\; the\; s</span>}}{{\mathrm{<span\; class="notranslate">\; the\; <figure-callout\; id="2"\; label="s"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">s</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; the\; <figure-callout\; id="2"\; label="s\; Rser"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">s</figure-callout></span><figure-callout\; id="2"\; label="s\; Rser"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">\; </figure-callout>}\frac{\mathrm{<span\; class="notranslate">\; </span>}}{}\frac{\mathrm{<span\; class="notranslate">Rser</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="lser"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">lser</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="lser"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">lser</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="Cser"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">Cser</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="Vtr"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">Vtr</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}$

$=\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">K</figure-callout>}2\frac{\mathrm{the\; s}}{{\mathrm{the\; <figure-callout\; id="2"\; label="s"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">s</figure-callout>}}^2+{2\mathrm{\&alpha;}}_1\mathrm{the\; s}+{{\mathrm{\&omega;}}_1}^2}\frac{\mathrm{the\; s}}{{\mathrm{the\; <figure-callout\; id="2"\; label="s"\; filenames="HDA00002312378800221.png,HDA00002312378800222.png"\; state="\{\{state\}\}">s</figure-callout>}}^2+{2\mathrm{\&alpha;}}_2\mathrm{the\; s}+{{\mathrm{\&omega;}}_2}^2}\mathrm{Vtr}1$ (Formula 6)

_α1 and _α2 are damping coefficients relating to the first ultrasonic transducer TR1 and the second ultrasonic transducer TR2 respectively, corresponding to damping parameters that can be found from the envelope of the summed supply current signal SCS+ described above.

ω ₁ and ω ₂ are the undamped angular oscillation frequencies of the first ultrasonic transducer TR1 and the second TR2 ultrasonic transducer, respectively. These undamped angular oscillation frequencies ω ₁ , ω ₂ used in the simulation formula and the corresponding The relationship between damped angular oscillation frequencies ω _D1 and ω _D2 is as follows:

${\mathrm{\&omega;}}_1=\sqrt{{\mathrm{\&omega;}}_{\mathrm{D.}1}^2+{\mathrm{\&alpha;}}_1^2}^{\mathrm{\&omega;}}_2=\sqrt{{\mathrm{\&omega;}}_{\mathrm{D.}2}^2+{\mathrm{\&alpha;}}_2^2}$ (Formula 7)

K2 is a proportionality factor that can be calculated. However, as with the specific component values of Cser1, Lser1, Rser1, Cser2, Lser2, Rser2 of the equivalent diagram in the last part of Figure 10, the value of K2 is not required to simulate the signal chain through the flowmeter using Equation 6.

The last expression of Equation 6, the differential equation for a circuit comprising two secondary oscillating circuits, can be simulated using well-known mathematical tools such as the Runge-Kutta method.

Figure 11 depicts some of the differences and similarities between the physical and simulated signal chains through a flowmeter according to the invention.

In simulating the signal chain, the physical transducers TR1, TR2 and their associated loads are modeled such as described above.

In the fully simulated signal chain in Figure 11, the output from the physical signal generator that filters the digital input signal from the signal controller and amplifies the filtered input by The signal is used as a driver for the first transducer TR1, where the output is filtered using a filter model of the signal generator before being used as an input function of the simulated transducer model. In another embodiment of the simulated signal chain, the input function of a simulated transducer model can be generated by recording the actual output from a physical signal generator or an analog-to-digital converter, thereby obtaining a part-physical, part-simulation model signal chain.

The electrical reception signal received by the receiver circuit and the signal processing later in the physical signal chain is only replaced by the signal processing in the simulated signal chain, which preferably includes a model of the receiver circuit (not shown in the figure) .

Therefore, if the signal function in the simulated signal chain does in fact correspond to the input signal from the signal controller in the physical signal chain, and if the filter model and transducer model of the signal generator and (optionally) receiver circuit It is appropriate that the only difference between the output of the final signal processing of the simulated signal chain and the output of the final signal processing of the physical signal chain is the time delay _td of the ultrasonic signal on the flow path FP, which is not part of the simulated signal chain.

The simulation model response is essentially the same as the physical flowmeter response, except for the time delay _td and possible amplification factors of the ultrasonic signal in the flow path FP, which allows very precise determination of This time delay t _d is made possible.

The first step in the method is to characterize the two transducers TR1 , TR2 by determining characteristic quantities such as the angular frequency ω _D and the damping parameter α of the damped oscillations of the transducers TR1 , TR2 described above.

Second, by using the known angular oscillation frequency ω of the transmission signal used in the flowmeter, equations 5-7 can be used to find an equivalent model for transducers TR1, TR2 and enable the establishment of transducers TR1, TR2 Digital simulation model and electronic circuit of the signal generator SG.

Third, the system can be simulated by entering a function of the input signal (or alternatively, a sampled version of the physically transmitted signal to the first transducer) into a digital simulation model, where if the two transducers TR1, Without a time delay in the transmission of the ultrasonic signals between TR2, the simulated model response, ie the model-according output signal from the receiver circuit RC, can be found.

In a fourth step of the method, the physical flowmeter response is recorded, ie the physical received signal actually received by the receiver circuit RC.

Finally, by determining the time delay of the physical flowmeter response compared to the simulated model response, the absolute transit time can be calculated.

Figure 13 depicts one embodiment of how calculating absolute transit times is performed according to the present invention.

According to the method described above, an input signal entered into the system results in a measured physical flowmeter response with a specified delay and a simulated model response with substantially no delay. As mentioned above, if the equivalent model of transducers TR1 , TR2 is appropriate, the two response signals will be substantially the same, except for the time delay, as shown in FIG. 13 .

Now, the absolute transit time, that is, the time delay between two signals, can be determined very precisely, for example by finding the filtered envelope of each of the two signals and determining the time difference between the two points, where the The filtered envelopes reach 50% of their maximum value respectively. This method for finding the absolute transit time is schematically depicted in FIG. 13 .

FIG. 14 depicts an equivalent diagram of the signal generator SG and the ultrasonic transducer TR connected thereto. Basically, the signal generator SG in FIG. 14 is of the type shown in FIG. 5 with feedback impedances Rfb, sg and filter impedance Rfilt, and the ultrasonic transducer TR is represented by the equivalent diagram depicted in FIG. 9 .

The active component OPsg of the signal generator SG is equipped with a current sense resistor RCC arranged in series with the aforementioned positive voltage supply VCC. The ultrasonic transducer TR is connected with the signal generator SG through a switch SW and bypassed by a voltage divider (bleeder) resistor Rbleed corresponding to R13 and R14 in FIG. 6 .

Using the graph in Figure 14 as a starting point, another method for determining the absolute transit time can be described, which is as accurate as the method described above, but is even more efficient in terms of the calculations required, and whose description is replaced by The characteristics of the impulse response of the transducer system, rather than the above-mentioned characteristics of the transducers TR1, TR2 themselves.

In this alternative method, the ultrasonic transducer Each of TR1, TR2 records a single pulsed supply current signal SPSCS1, SPSCS2.

The difference from the previous approach is that in this case the digitally pulsed input signal DPSa, DPSb has been replaced by a single pulse such as that shown in Fig. 15a, which results in a single power supply for the two transducers TR1, TR2 respectively The current signals SPSCS1 and SPSCS2 are shown in Fig. 15b and Fig. 15c.

It is evident that the first oscillation of each of the two single-pulse supply current signals SPSCS1, SPSCS2 is somewhat distorted. This is due to the fact that the entire current provided by the active component OPsg which is not the signal generator SG passes through the oscillating circuits Lser, Cser, Rser which are equivalents of the ultrasound transducers TR1, TR2 respectively. In order to find the single pulse response SPSCS1, SPSCS2 of these oscillating circuits, the current through the two impedances Rfb, sg and Rfilt and the capacitance Cpar must be removed from the single pulse supply current signal SPSCS1, SPSCS2.

The current through Rfb, sg, which are connected to the virtual ground, can be easily found by opening the switch SW as shown in Figure 14 and repeating the measurement without any ultrasonic transducers TR1, TR2 connected to the signal generator . This results in a single pulse supply current signal SPSCS0, shown in Figure 15d, which is proportional to the single pulse SP in Figure 15a due to the fact that Rfb, sg are ohmic resistors.

Measuring the current through Rfilt is not as easy as measuring the current through Rfb, sg. However, since Rfilt is an ohmic resistance to ground in parallel with Rfb, sg, when the ratio between Rfb, sg, and Rfilt is known, and it is possible to transfer two current signals from two ultrasonic transducers TR1, TR2 When subtracted from each of the single pulse supply current signals SPSCS1, SPSCS2, the current through Rfilt can thus be easily calculated from SPSCS0.

For the current through Cpar, it includes a transient spike coincident with the leading edge of the single pulse SP and another transient spike of opposite polarity coincident with the trailing edge of the single pulse SP. These spikes have a short duration compared to the oscillation period of the single pulsed supply current signals SPSCS1, SPSCS2 of the two ultrasonic transducers TR1, TR2, so that the single pulsed supply current can be easily subtracted by simple interpolation Each of the signals SPSCS1, SPSCS2.

The calculated The single pulsed supply current signals SPSCS1 , SPSCS2 of the two ultrasound transducers TR1 , TR2 , wherein the single pulsed supply current signals SPRTR1 , SPRTR2 look similar to those described in Figures 16a and 16b.

It can be found that the calculated single impulse response SPRSYS for the entire ultrasonic transducer system as shown in Figure 16c is the convolution of the single impulse responses SPRTR1, SPRTR2 of the two ultrasonic transducers TR1, TR2, and described in Figure 16c similar to.

By repeating the calculation of a single impulse response SPRSYS with a suitable delay multiple times, it is possible to calculate a simulated flowmeter response corresponding to an input signal comprising multiple pulses, which is very similar to the actual measured flowmeter response except for the time delay of the latter Furthermore, this is due to the transit time between the two ultrasonic transducers TR1, TR2. Figures 17a and 17b depict the simulated flowmeter response RESPem and the corresponding measured flowmeter response RESPms, respectively.

Absolute transit times can be determined by comparing the filtered envelopes of the simulated and measured meter responses, respectively, as schematically depicted in Figure 13 and explained above, or they can be determined by using the Fast Fourier leaf transform (FFT) to determine.

In the time domain, the estimated flowmeter response z’(t) can be calculated from the following formula:

z′(t)=y ₁ (t)*y ₂ (t)*x(t) (Equation 8)

where y ₁ (t) and y ₂ (t) are the calculated single impulse responses of the two ultrasonic transducers TR1, TR2, respectively, represented by the two signals SPSCS1 and SPSCS2 in Fig. 16a and Fig. 16b, and x( t) is the input signal at the input of the active component Opsg of the signal generator SG.

It should be noted that in Equation 8 above, the symbol '*' is used as an operator indicating the convolution of the signal around it, which is not to be confused with the multiplication operation usually indicated by the same symbol.

In the time domain, the relationship between the estimated flowmeter response z’(t) and the measured flowmeter response z(t) is:

z(t)≈z′(tt _d ) (Equation 9)

where _td is the time delay of the ultrasonic signal in the flow path FP.

This reflects that the measured flowmeter response and the estimated flowmeter response are nearly identical, except for the time delay _td for the former.

If the estimated response is ideal, this means that, in the frequency domain, the magnitude of the measured meter response z(s) and the estimated magnitude of the meter response Z'(s) should be the same for all frequencies, as shown in Figure 18a shown.

In addition, the phase angle between Z(s) and Z'(s) changes linearly with frequency, as shown in Figure 18b. The slope of the line in Figure 18b is the group time delay, corresponding to the ultrasonic signal in the flow path FP time delay t _d .

Figure 19 shows the above estimated actual meter response RESPem and the corresponding actual measured meter response RESPms in the same path to show the similarity of the two signals and the time delay between them.

The magnitudes |Z'(s)| and |Z(s)| in the frequency domain for the two flowmeter responses corresponding to RESPem and RESPms respectively are shown in Figures 20a and 20b, respectively. Although similar, it is clear that the two graphs do not fully agree, indicating that the estimated meter response RESPem deviates slightly from the measured meter response RESPms even though the time delay is ignored.

The phase angle between Z(s) and Z'(s) at different frequencies is depicted in Fig. 21a. In theory, this graph should correspond to the graph shown in Figure 18b, but clearly this is not the case.

However, looking closely at Figure 21a, the two graphs are not as different as they appear at first glance. Conversely, the graph in Figure 18b is linear, and the graph in Figure 21a can be generalized to a sawtooth-like character, since the phase angles in this graph are "packed" to fall into the range from -πrad to +πrad .

It is evident that the sawtooth shape of the graph in Fig. 21a is covered by a certain amount of noise, mainly due to small magnitudes of Z(s) and/or Z'(s) affecting the calculation at some frequencies. However, the portion of the graph between the two dashed lines is very close to linear, where the portion of the graph corresponds to a frequency range with large amplitudes of Z(s) and Z'(s), as can be seen from Figures 20a and 20b. Figure 21b shows a magnified portion of the portion of the graph in Figure 21a. It should be noted that the slope of the linear part can be calculated by finding the phase angle between Z(s) and Z'(s) for only two different frequencies.

The slopes of the graph in Fig. 21b at different frequencies are shown in Fig. 22, where the slope corresponds to the time delay t _d of the ultrasonic signal in the flow path FP. The time unit on the vertical axis of the graph corresponds to the oscillation period of the transmission signal RESPms. Thus, according to FIG. 22 , the measured flow meter response RESPms is delayed by 2.3 oscillation periods compared to the simulated flow meter response RESPem, which is preferably suitable for the two signal curves shown in FIG. 19 .

It should be noted that the change of the calculated time delay _td , that is, the slope of the graph in Figure 22, is only a few percent of the oscillation period, which means that compared with other known methods in the prior art, The time delay t _d calculated by this method has a high precision.

In practice, the actual meter response RESPms is best measured using a transmitted signal comprising multiple pulses, while the simulated meter response RESPem is most easily calculated by suitable digital filtering of the single impulse response SPRSYS calculated above. This has no effect on the results obtained by this method.

By using the method described above, the absolute transit times corresponding to _t1 and _t2 in Equation 1 can be determined with high absolute accuracy independently of the transducer parameters (down to about 100 ns for a 1 MHz transducer, Significantly improved accuracy compared to possible all previously known systems).

Typically, flow meters according to the invention perform flow metering at regular time intervals, typically in the range between 0.1 seconds and 5 seconds. It should be noted, however, that the characterization of the transducer or transmitted signal and the simulation of the flowmeter system need not be repeated for each flow metering performed by the flowmeter, for example, in order to extend the life of the battery powering the flowmeter.

Due to the aging of the transducers TR1, TR2, the characteristics of the transducers change slowly over time and become more spontaneous due to changes in the temperature of the fluid in the flow path FP in which they are arranged.

Thus, by using new transducer characteristics or signal characteristics in calculating the absolute time-of-flight and determining the updated simulation model of the flowmeter system at regular predetermined time intervals and/or when a temperature change is detected outside certain predetermined limits is Advantageously, since the speed of ultrasound is dependent on the temperature of the medium through which the ultrasound is transmitted, the change in temperature is indicated by the change in the calculated transit time.

Due to the high cost (and high power consumption) of very high speed analog-to-digital converters, it is advantageous to use slower converters in flow meters according to the invention. However, it is well known from Nyquist theory that an analog signal without specific distortions cannot be reconstructed if the signal is sampled at a frequency lower than twice the maximum frequency present in the signal.

Consequently, if a low sampling frequency is used to record the electrical receive signal received by the receiver circuit of a flow meter according to the invention, the physical flow meter response signal will be distorted. However, if the simulated model response is subjected to the same undersampling, similar distortions of this signal will occur, and the two response signals can still be compared to find a very accurate measure of the absolute transit time mentioned above.

Known spectral sequences that undersample continuous signals are schematically depicted in Figs. 23a-c.

Figure 23a depicts an example of a spectrum of a continuous signal, and Figure 23b depicts how undersampling (in this case a sampling frequency of 5/6 of the signal frequency) leads to the creation of an infinite number of aliases of the original spectrum.

Fig. 23c schematically depicts how an undersampled signal is reconstructed by changing the sampling frequency to the Nyquist sampling frequency fs2 and filtering the signal with a FIR reconstruction filter, the frequency bands of which are shown in the figure.

The distortion of undersampled continuous signal reconstruction is schematically depicted in Figs. 24a-b and Figs. 25a-b.

Figure 24a depicts an embodiment of a continuous signal, and Figure 24b depicts digital samples obtained by sampling the continuous signal of Figure 24a at a sampling frequency of 5/6 of the signal frequency.

Figure 25a depicts the reconstruction of the signal of Figure 24a using a wideband FIR reconstruction filter, while Figure 25b depicts the reconstruction of the same signal using a narrowband FIR reconstruction filter.

By comparing the reconstructed signal shown in Figure 25a and Figure 25b with the original signal shown in Figure 24a, it is evident that using a narrowband FIR reconstruction filter compared to using a wideband FIR reconstruction filter would result in more serious distortion. The preferred bandwidth of the FIR reconstruction filter to use depends partly on the width of individual folds in the undersampled spectrum and partly on the amount of noise in the signal.

Fig. 26 schematically depicts a method for finding the magnitude and phase of an undersampled continuous signal without using any FIR reconstruction filter.

The upper part of FIG. 26 includes two frames, respectively showing a continuous signal and digital samples obtained by sampling the continuous signal at a sampling frequency of 5/6 of the signal frequency.

The relationship between signal frequency and sampling frequency means that for every six oscillations of the continuous signal, 5 samples are collected. If the continuous signal is stationary, then 5 samples from a period of 6 oscillations would correspond exactly to 5 samples from the preceding 6 oscillations and 5 samples from the following 6 oscillations.

If a relatively long input signal is used, the very middle part of the signal can be considered to be substantially stationary, as shown in the upper part of Fig. 26, and thus it is possible to pick out samples obtained from this part of the signal and , where each group consists of multiple “similar” samples from different time periods of 6 oscillations of the continuous signal, as shown in the bottom half of Figure 26.

If the sorting and summarization of the samples is done in a suitable manner, these 5 groups of samples together form an "average sample" of a single oscillation, which corresponds to a single oscillation of a substantially stationary part of a continuous signal, and thus by the digital Fourier The transform DFT is capable of determining the magnitude and phase of a continuous signal.

As mentioned above, the difference between the transit times of two different ultrasonic signals can be easily found by comparing the phases corresponding to the two electrical receive signals received by the receiver circuit RC of the flowmeter, where the difference corresponds to Equation 1 The amount in (t ₁ -t ₂ ). Thus, in order to find this difference in systems using undersampling, preferably the transmitted signal should be relatively long, ensuring that there is enough information in the samples of substantially stationary parts of the signal to determine the phase of the signal with sufficient precision.

Fig. 27 schematically depicts a method for reconstructing an undersampled continuous signal without distortion.

Again, the continuous signal shown in the upper part of Fig. 27 is sampled with an analog-to-digital converter operating at a sampling frequency of 5/6 of the signal frequency. However, in this method, the signal is transmitted and sampled 6 times, the replacement sampling timing corresponds to 1/5 of the oscillation period of the continuous signal, and the resulting 6 sets of interleaved samples obtained from this sampling are shown in Fig. 27 The middle is schematically depicted.

By appropriately combining the interleaved samples, samples corresponding to a sampling frequency 5 times the signal frequency can be obtained. Only 2 times the signal frequency is needed (according to Nyquist's law), which is enough to reconstruct the signal without distortion.

In order to determine precise values of the absolute transit times t ₁ and t ₂ to add together to obtain the quantity (t ₁ +t ₂ ) in Equation 1, the transmission signal should preferably be relatively clear, short and well-defined.

Considering the above reasons, in order to obtain very accurate values of the absolute transit time, digital signal processing on the physical and simulated model responses of the flowmeter according to the invention should be performed as schematically described in FIG. 28 .

First, if the signal is undersampled, oversampling and anti-aliasing filtering are performed in order to reconstruct the signal.

Subsequently, arbitrary filtering, including bandwidth limiting, can be performed in order to improve the signal-to-noise ratio of the signal.

A relatively clear, short and well-defined transmitted signal is simulated from the actual received and filtered signal in two steps, where the transmitted signal is advantageous for obtaining very precise absolute transit time determinations (see above):

The first simulation step consists in obtaining a simulated substantially stationary signal by adding a delayed version of the received signal to the signal itself. For example, if the transmitted signal includes 5 oscillations, the received and filtered versions of the signal (which are delayed by 5, 10, 15 and other signal periods) are added to the actual received and filtered signal. Due to the overall linearity of the system, if the transmitted signal consists of 10, 15, 20 and other periods of oscillation, the principle of superposition ensures that the resulting signal is exactly similar to the received filtered version of the signal.

The second simulation step includes subtracting the delayed version of the simulated substantially stationary signal from the simulated substantially stationary signal itself. For example, if the subtracted signal is delayed by 2 signal periods, and if the transmitted signal consists of 2 oscillation periods, the superposition principle ensures that the resulting signal is exactly similar to the already received filtered version of the signal. If this subtraction was done with 2 versions of the original received signal and the filtered signal corresponding to the transmitted signal comprising only 5 oscillation periods, the resulting signal would be the same as with two pulses followed by a pause of 3 oscillation periods , and followed by a signal corresponding to the transmitted signal of another 2 pulses with opposite phases of the first 2 pulses. Obviously, such an odd signal is very unsuitable for this purpose.

Now, calculate the envelope of the simulated short signal and obtain the point in time at which 50% of the envelope maximum has been reached, as shown in Figure 13.

Finally, the absolute transit time is determined by subtracting the corresponding time points associated with the envelope of the simulated model response signal calculated from the transducer characteristics described above.

It should be noted that the scope of the present invention should never be construed as being limited to the above-mentioned embodiments of the present invention, and the above-mentioned embodiments of the present invention should only be regarded as examples of multiple embodiments falling within the scope of the present invention. The scope of the invention is defined by the following patent claims.

List of reference signs

CC. Common conductors for signal generator and receiver circuits

Cconn. The capacitor connected between the signal generator power supply and the receiver circuit

Cpar. The parallel capacitor in the equivalent diagram of the ultrasonic transducer

Cpar1. Parallel capacitance in the equivalent diagram of the first ultrasonic transducer

Cpar2. Parallel capacitance in the equivalent diagram of the second ultrasonic transducer

Cser. The series capacitor in the equivalent diagram of the ultrasonic transducer

Cser1. The series capacitor in the equivalent diagram of the first ultrasonic transducer

Cser2. The series capacitance in the equivalent diagram of the second ultrasonic transducer

DFT. Digital Fourier Transform

DPSa. The first digital pulse input signal

DPSb. The second digital pulse input signal

Escs. The envelope of the power supply current signal

FP. Flow path of fluid flow

fs. undersampled frequency

fs2. Nyquist sampling frequency

Itr1. The current through the first transducer in the equivalent diagram

Itr2. The current through the second transducer in the equivalent diagram

Lser. Series inductance in the equivalent diagram of an ultrasonic transducer

Lser1. Series inductance in the equivalent diagram of the first ultrasonic transducer

Lser2. Series inductance in the equivalent diagram of the second ultrasonic transducer

OP. Operational amplifier common to signal generator and receiver circuits

OPrc. Operational amplifier in receiver circuit

OPrc1. Operational amplifier in the first receiver circuit

OPrc2. Operational amplifier in the second receiver circuit

OPsg. Operational amplifier in signal generator

Rbleed. Divider resistance of ultrasonic transducer

RC. Receiver circuit

RCC. Current sense resistor for supply current

Rconn. Resistor connected between signal generator power supply and receiver circuit

RESPem. Simulated flow meter response

RESPms. Measured flowmeter response

Rfb, sg. Feedback resistor in signal generator

Rfilt. Filter resistance

Rser. The series resistance in the equivalent diagram of an ultrasonic transducer

Rser1. The series resistance in the equivalent diagram of the first ultrasonic transducer

Rser2. The series resistance in the equivalent diagram of the second ultrasonic transducer

SCSa. The first part of the supply current signal

SCSb. The second part of the supply current signal

SCS-. Subtract the power supply current signal

SCS+. Add power supply current signal

SG. Signal Generator

SP. Single pulse

SPRSYS. Single impulse response of a system

SPRTR1. Single impulse response of the first ultrasonic transducer

SPRTR2. Single Impulse Response of Second Ultrasonic Transducer

SPSCS0. Single pulsed supply current signal without any ultrasonic transducer

SPSCS1. Single pulse power supply current signal of the first ultrasonic transducer

SPSCS2. Single pulse power supply current signal for the second ultrasonic transducer

SPU. Signal Processing Unit

SU. Switching unit

SW. switch

SW1. First switch

SW2. Second switch

SWconn. A switch for the connection between the signal generator power supply and the receiver circuit

t _d . Time delay of the ultrasonic signal in the flow path

Tscs. The oscillation period of the power supply current signal

TR1. The first ultrasonic transducer

TR2. Second ultrasonic transducer

TR. Ultrasonic transducer

VCC. Positive power supply

Vtr1. The voltage applied to the first transducer in the equivalent diagram

Vtr2. The voltage applied to the second transducer in the equivalent diagram

Zad. Adaptive Impedance

Zfb. Feedback impedance in combined signal generator and receiver circuits

Zfb, rc. Feedback impedance in receiver circuits

Zfb, rc1. Feedback impedance in the first receiver circuit

Zfb, rc2. Feedback impedance in the second receiver circuit

Zfb, sg. Feedback Impedance in Signal Generators

Zfilt. Filter impedance

Zsig. Signal impedance

α1. Damping parameters related to the first ultrasonic transducer

α ₂ . Damping parameter associated with the second ultrasonic transducer

ω ₁ . Undamped angular oscillation frequency of the first ultrasonic transducer

ω ₂ . Undamped angular oscillation frequency of the second ultrasonic transducer

ω _D1 . Damped angular oscillation frequency of the first ultrasonic transducer

ω _D2 . Damped angular oscillation frequency of the second ultrasonic transducer

Claims (22)

1. A method for determining the absolute transit time ( _td ) of an ultrasonic signal in a flow path (FP) of an ultrasonic flowmeter comprising two ultrasonic transducers (TR1, TR2), said method comprising the following step: Monitoring of active components ( OPsg) to drive the current of the transducer (TR1; TR2) to obtain the supply current signal (SPSCS1; SPSCS2) for the transducer (TR1; TR2; SCSa, SCSb), If there is no time delay in the transmission of the ultrasonic signal between the two ultrasonic transducers (TR1, TR2), the flowmeter response (RESPem) similar to the output signal from the receiver circuit (RC) of the flowmeter is simulated to As an output signal, Comparing the simulated meter response (RESPem) with the measured meter response (RESPms) actually received by the receiver circuit (RC), and The absolute transit time (t _d ) is calculated as the time difference between the simulated meter response (RESPem) and the measured meter response (RESPms). 2. The method of claim 1, wherein the step of simulating the flowmeter response (RESPem) comprises: A single pulse input signal (SP) is supplied to a signal generator (SG) comprising active components (OPsg) to drive the transducers (TR1; TR2), During or after the input signal (SP) is supplied to the signal generator (SG), the current from one or more voltage supplies (VCC; V3) to the active components (OPsg) is monitored to obtain The single pulse power supply current signal (SPSCS1; SPSCS2) of the device (TR1; TR2), Conditioning single pulse supply current signals (SPSCS1; SPSCS2) and obtaining simulated single pulse responses (SPRTR1; SPRTR2) of transducers (TR1; TR2), Repeat the previous three steps for the other transducers (TR2; TR1) to obtain another simulated single impulse response (SPRTR2; SPRTR1), Find the single impulse response of the system (SPRSYS) by convolving the two obtained single impulse responses (SPRTR1; SPRTR2) of the transducers (TR1, TR2), and The simulated flowmeter response (RESPem) is calculated by combining multiple instances of the found single impulse response (SPRSYS) of the system, which are repeated with suitable delays. 3. The method of claim 1, wherein the step of simulating the flowmeter response (RESPem) comprises: A pulsed input signal (DPSa, DPSb) is supplied to a signal generator (SG) comprising active components (OPsg) to drive a transducer (TR1; TR2), During or after the input signal (DPSa, DPSb) is supplied to the signal generator (SG), the current from one or more voltage supplies (VCC; V3) to the active components (OPsg) is monitored to obtain one or more Multiple supply current signals (SCSa; SCSb), From one or more source current signals (SCSa, SCSb) obtained or from one or more generated signals (SCS-, SCS+) derived from one or more source current signals (SCSa, SCSb), directly determine one or more quantities used to characterize the transducer (TR1; TR2), Repeat the previous three steps for the other transducers (TR2; TR1) to obtain similar quantities characterizing the other transducers (TR2; TR1), Use the determined characteristic quantities of the transducers to find equivalent models of the transducers (TR1, TR2) and build the transducers (TR1; TR2) and signal generators (SG) and/or receivers of the flowmeter multiple simulation models of the electronic circuit of the circuit breaker (RC), and A simulated flowmeter response is obtained by simulating the flowmeter system by entering a functional or sampled version of the input signal of the physically transmitted signal to the first transducer into a digital simulation model. 4. A method according to claim 3, wherein the quantities used to characterize the transducers (TR1, TR2) comprise: from the acquired signals (SCSa, SCSb) and/or derived signals (SCS-, SCS+) At least a portion of one or more determined oscillation periods (Tscs) and/or damping parameters (α), said signal portions represent damped oscillations. 5. A method according to any one of claims 2 to 4, wherein by monitoring one or more voltage supplies across the active components (OPsg) in the signal generator (SG) and the signal generator (SG) One or more supply current signals (SPSCS1, SPSCS2; SCSa, SCSb) are obtained from the voltage on one or more current sense resistors (RCC, R8; R43) arranged in series between (VCC, V3). 6. A method according to any preceding claim, wherein the step of calculating an absolute time-of-flight comprises: For example, the simulated flowmeter response (RESPem) and the measured flowmeter response (RESPms) are converted to the frequency domain by fast Fourier transform, determining a phase angle between two flowmeter responses at at least two different frequencies in the frequency domain, and The absolute transit time ( _td ) was determined by calculating the group time delay from the two determined phase angles. 7. A method according to any one of claims 1 to 5, wherein the step of calculating the absolute time-of-flight comprises: Find the filtered envelopes of the simulated meter response (RESPem) and the measured meter response (RESPms) separately, separately identify two points in time where the filtered envelope reaches 50% of their maximum value, and The absolute transit time (t _d ) is calculated as the time difference between the two identified points in time. 8. An ultrasonic flowmeter comprising at least one ultrasonic transducer (TR1) and a signal generator (SG) for generating an electrical signal to the transducer (TR1), said signal generator (SG) comprising active components (OPsg), It is characterized by The flow meter further includes means for measuring one or more supply currents to active components of the signal generator. 9. A flow meter according to claim 8, wherein the means for measuring one or more supply currents comprises: a resistor inserted in series between the source of the positive supply voltage (V3; VCC) and the active component (OPsg) (R8; RCC) and/or a resistor (R43) inserted in series between the source of the negative supply voltage and the active component (OPsg). 10. A method for characterizing an ultrasound transducer (TR1, TR2), said method comprising the steps of: A pulsating input signal (DPSa, DPSb) is supplied to a signal generator (SG) to drive a transducer (TR1, TR2), said signal generator comprising active components (OPsg), During or after the input signal (DPSa, DPSb) is supplied to the signal generator (SG), the current from one or more voltage supplies (VCC; V3) to the active components (OPsg) is monitored to obtain one or more Multiple supply current signals (SCSa, SCSb), and from one or more derived supply current signals (SCSa, SCSb) or from one or more generated signals (SCS-, SCS+) derived from one or more derived supply current signals (SCSa, SCSb), directly One or more quantities describing the characteristics of the transducers (TR1, TR2) are determined in a precise manner. 11. A method according to claim 10, wherein by monitoring one or more voltage supplies (VCC, V3) across the active components (OPsg) of the signal generator (SG) and the signal generator (SG) One or more supply current signals (SCSa, SCSb) are obtained from the voltage across one or more current sense resistors (RCC, R8; R43) arranged in series. 12. A method according to claim 10 or 11, wherein the quantities used to characterize the transducers (TR1, TR2) comprise obtained signals (SCSa, SCSb) and/or derived signals (SCS−, SCS+ Oscillation periods (Tscs) and/or damping coefficients (α) determined by at least a portion of one or more of ), said signal portions representing damped oscillations. 13. A method for determining the time delay of an ultrasonic signal in a flow path (FP) of an ultrasonic flowmeter, the method comprising the steps of: Describe the characteristics of the two transducers TR1, TR2 of the flowmeter by determining characteristic quantities such as the damping coefficient α and the angular frequency ω _D of the damped oscillations of the transducers TR1, TR2, Using the determined characteristic quantities of the transducers, an equivalent model of the transducers TR1, TR2 is found and the digital circuits of the signal generator SG and/or the receiver circuit RC of the flowmeter and the transducers TR1, TR2 are established simulation model, The flowmeter system is simulated by entering into the digital simulation model a functional or sampled version of the input signal of the physically transmitted signal arriving at the first transducer, if the transmission of the ultrasonic signal between the two transducers TR1, TR2 With no time delay in , the simulated model response corresponding to the output signal from the receiver circuit RC according to the model is obtained, record the physical flowmeter response actually received by the receiver circuit RC, and The absolute transit time is calculated by determining the time delay of the physical flowmeter response compared to the simulated model response. 14. The method of claim 13, wherein the step of calculating the absolute time-of-flight comprises the steps of: Find the filtered envelopes of the simulated model response and the physical flowmeter response, respectively, separately identify two points in time where the filtered envelope reaches 50% of their maximum value, and The absolute transit time is calculated as the time difference between two identified points in time. 15. An ultrasonic flowmeter comprising at least one ultrasonic transducer (TR1) and a signal processing unit (SPU) for processing electrical signals received from at least one ultrasound transducer (TR1), It is characterized by The signal processing unit is arranged to digitize the continuous signal from the at least one ultrasound transducer ( TR1 ) at a sampling frequency which is twice the resonance frequency of the at least one ultrasound transducer ( TR1 ). 16. An ultrasonic flowmeter comprising Flow path (FP) for fluid flow, at least two ultrasonic transducers (TR1, TR2) acoustically coupled to the flow path, wherein one transducer (TR1) is arranged upstream of the other transducer (TR2) along the flow path, A signal generator (SG) for generating the electrical transmission signal to the transducer, the signal generator (SG) includes a negative feedback coupled operational amplifier (OP; OPsg), A receiver circuit (RC) for receiving the electrical receive signal from the transducer, the receiver circuit (RC; RC1, RC2) includes a negative feedback coupled operational amplifier (OP; OPrc; OPrc1, OPrc2), a switching unit (SU) for switching the electrical transmission signal between the signal generator and the transducer and for switching the electrical reception signal between the transducer and the receiver circuit, a signal processing unit (SPU) for providing an output indicative of the flow rate on the flow path based on the electrical receive signal, It is characterized by the switching unit is coupled to the output of the operational amplifier of the signal generator, and The switching unit is coupled to the inverting input of the operational amplifier of the receiver circuit. 17. A flow meter according to claim 16, wherein the output impedance of the signal generator and the input impedance of the receiver circuit are negligible compared to the impedance of the transducer, for example less than 10 ohms, preferably less than 1 ohm , more preferably less than 0.1 ohms. 18. A flow meter according to claim 16 or 17, wherein the signal generator and receiver circuits share at least one active component. 19. A flow meter according to claim 16 or 17, wherein all active components of the signal generator are fully isolated from all active components of the receiver circuit. 20. A flow meter according to any one of claims 16 to 19, wherein one or more operational amplifiers in the signal generator and receiver circuit are current feedback operational amplifiers. 21. A flow meter according to any one of claims 16 to 20, wherein the one or more operational amplifiers in the signal generator and receiver circuits operate with an input common mode voltage whose AC component is substantially zero or Negligible at least. 22. A flow meter according to any one of claims 16 to 21, wherein at least two transducers are arranged to transmit ultrasonic signals simultaneously.

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